Foot-and-Moutli Disease. 95 



because the germ in (luestion is difficult to grow outside the 

 body, and (2) 'oecause if it had been one half smaller than it 

 actually is its discovery, inUhe sense of being able to see it, 

 would have been impossible. 



Fia. 2.— Showing near the tip of the tongue a circular sore left after bursting of 

 a vesicle. The sore is in process of healing. 



A yrlori reasoning might thus have led to the conclusion 

 that in all probability some germs or bacteria are too small to 

 be made visible to the eye of man, and at the present time it is 

 actually assumed that the causes of some diseases, although 

 living things which grow and multiply, have escaped detection 

 because they lie beyond the limits of visibility. Foot-and- 

 mouth disease is one of these diseases, and the belief that its 

 cause is an invisible germ is founded on the following facts. 

 The thing which is the cause of foot-and-mouth disease is 

 present in the nearly clear watery liquid of the vesicles or 

 blister-like lesions which are formed in the mouth during the 

 course of an attack. That is proved by the fact that this 

 liquid can be successfully employed to infect an animal with 

 the disease. Furthermore, the cause is abundantly present in 

 the liquid, for it has been found (Loeffler) that ^tjcoo part of a 

 cubic centimetre of it will infect an ox when injected into 

 a vein. 



